1. Field of the Invention
The present invention relates to an optical imaging device for optically forming images of objects.
2. Related Art
There has heretofore been known an optical imaging device comprising a convex roof-shaped mirror, a lens array, and a concave roof-shaped mirror array that are housed in a casing having entrance and exit apertures. Light from an object to be imaged is introduced through the entrance aperture of the casing, then guided successively via the convex roof-shaped mirror, the lens array, the concave roof-shaped mirror array, the lens array, and the convex roof-shaped mirror, and finally delivered out through the exit aperture to register the image of the object in a given position.
The conventional optical imaging device has a spacer interposed between the concave roof-shaped mirror array and the lens array to space them apart from each other. The spacer is in the form of a slender plate held in engagement with upper and lower covers of the casing. The spacer serves as a reference member for arranging the lens array and the concave roof-shaped mirror array in proper positional relationship to each other. The slender spacer introduces problems in that it is liable to be deformed due to warping in its longitudinal direction. When the slender spacer is deformed, the lens array and the concave roof-shaped mirror array are also caused to be deformed, resulting in a curvature of the image plane on which the combined object image is formed and hence a distortion of the formed image.
Where the optical imaging device of the prior design is incorporated in a copying machine, flare light coming from a document or original to be copied onto the photosensitive body through the optical imaging device tends to fall on an area of the photosensitive body which should not be exposed to light.
More specifically, light from the document is dispersed in every direction due to diffused reflection by the document. Some reflected light rays enter through the entrance aperture, are reflected directly by the surface of the lens array, and then directed through the exit aperture toward the photosensitive body to expose an undesirable area thereof. The unwanted exposure of the photosensitive body produces different shades on the formed image, which is then lowered in quality.
The document to be copied is illuminated by one or two illuminating light sources disposed along the entrance aperture of the casing of the optical imaging device. If two illuminating light sources are positioned along the opposite edges of entrance aperture, a sufficient amount of illuminating light can be generated, but the space for installing the illuminating light source is increased. In case only one illuminating light source is located along one edge of the entrance aperture, the light source must be of a large capacity to produce a desired amount of illuminating light, though no large installation space is necessary.
The illuminating light emitted from the light source is required to be detected and controlled at all times since the light source is apt to deteriorate by aging and there are small characteristic variations from light source to light source. For such light control, it has been customary to detect light which is not directly involved in the illumination of a document to be copied. However, an installation space and a mechanism are required for a sensor which detects the amount of illuminating light.